PNEUMATIC CONVEYING is the utilization of the conveying power of air in motion. It will be realized that con veyance of material through a pipe-line, either by suction or blast, is ideal; since there are 130 mechanical parts in the path of the material there cannot be any contamination by lubrication. Another advantage is the greater flexibility of pneumatic plant; every part of the hold of a vessel, for instance, can be reached by flexible tubes for the purpose of unloading a grain cargo, whereas a more complex mechanical plant is rigidly fettered to straight lines.
The modus operandi of a pneu matic plant is extremely simple and is as follows :—Into a grain cargo in a vessel, for instance, a hosepipe is lowered, the nozzle at the end of which admits a mixture of air and grain. The other end of the pipeline enters tangentially into the upper part of a cylindrical receiver from which the air is exhausted, while the grain is withdrawn from the cone-shaped lower end by an air-trap, without, however, admit ting air into the receiver. When comparing pneumatic with mechanical handling devices the former have but one drawback, viz.: the greater consumption of driving power for handling a given quantity. This, however, is more than compensated for by the greater flexibility and the hygienic value of the system. The first grain handling installation on the Duckham system was known as "Mark Lane No. 1," and was built, under the personal supervision of the inventor, by the East Ferry Road Engineering Co., during the closing years of the 19th century. This was one of the most epoch-making revelations of all systems of handling.
The plant is mounted on a pontoon and sucks the grain through a nozzle and pipeline from the ship's hold to an elevated receiver, whence it runs by gravity to a given point, via an air trap; an exhauster furnishes a partial vacuum by pipes connected with the said receiver.
As has been shown, the material in a pneumatic plant floats, so to speak, in a current of air, from which it is separated by its specific gravity when the air expands in the receiver. The heavier the material to be handled the greater must be the speed of travel of the air in the conveying pipes in order to ensure the floating of the material in and with the air. If the air speed is too slow the tendency will be for the material to separate from the air and thus block the pipes, especially such portions as are horizontally disposed, or nearly so. Obviously, therefore, instal lations for such heavy materials as coal and ash require more powerful pumps. Similar installations in which, however, draught is induced by "steam jets" are successfully employed for han dling ash from boilers.
Owing to the advantages accruing from the use of pneumatic handling plants new avenues for their employment are being constantly opened. Such varied materials as grain, small coal, chemicals, ashes, potatoes, and even red-hot rivets and artillery shells are now successfully handled by pneumatic means. An offshoot of this system is the pneumatic tube, which is largely employed in postal and telegraph offices, as well as in great variety in business offices and stores. (G. F. Z.)